In a mobile communication system, the radio environment of a radio base station changes when a building is constructed around of the radio base station or the installation conditions of neighboring base stations of the radio base station change. For this reason, operators have been heretofore conducting drive tests by measuring and correcting radio environments by use of a measurement vehicle equipped with measurement equipment.
Such measurement and collection of the radio environments can contribute to optimization of parameters of a radio base station or the like, but have problems of requiring a large number of man-hours and high cost. For this reason, the 3GPP (3rd Generation Partnership Project) that is the standardization project of a mobile communication system has been developing the specifications of MDT (Minimization of Drive Test) (see, 3GPP TR 36.805 V9.0.0 “Study on Minimization of drive-tests in Next Generation Networks”, 2009-12 and 3GPP TS 37.320 v0.7.0, “Radio measurement collection for Minimization of Drive Tests (MDT)”, 2010-07). The MDT is a technology in which the measurement and collection of the radio environments are automated using radio terminals held by users.
One type of MDT, that is, a log-type MDT (referred to as a Logged MDT) is assumed to measure and collect a radio environment in the following methods. Firstly, a network including a radio base station sends a radio terminal a measurement configuration message for setting a measurement configuration. The measurement configuration contains a measurement trigger and the like. Then, the radio terminal in an idle mode (in other words, in a stand-by mode) measures a radio environment in accordance with the measurement configuration set by the measurement configuration message received from the network, and stores the measurement result.